This invention relates to angular rate-sensing devices, and specifically to an improved vibrating circular cylinder design useful in such devices.
The advantages of vibratory gyroscopes over the traditional design based upon a wheel supported in a gimbal are well known.
Numerous designs of vibratory gyroscopes have been produced and/or proposed. These include, among others: the tuning fork (see, for example, U.S. Pat. Nos. 4,524,619 (Reissue No. 32,931) and 4,899,587 to Staudte and U.S. Pat. No. 4,898,032 to Voles); the vibrating shell (e.g., Delco Resonator Gyro Key to New Inertial Systems, Aviation Week & Space Technology, (Sep. 30, 1991)); the vibrating beam (e.g., Vibrating Angular Rate Sensor, Electronics (June 1968); the vibrating disc (e.g., The Theory of a Piezoelectric Disc Gyroscope, IEEE Transactions on Aerospace and Electronic Systems (Vol. AES-22, No. 4, July 1986); and the vibrating cylinder (e.g., The Dynamics of a Thin Piezoelectric Cylinder Gyroscope, Proc. Instn. Mech, Engrs. (Vol. 200, No. C4).
The above-referenced Delco Resonator Gyro is a hemispherical resonator gyro that has been nicknamed "the wineglass gyroscope" because of the shape of its resonating element. As described herein, my present invention may correspondingly be nicknamed "the beermug gyroscope".
The "wineglass" and cylinder gyroscopes mentioned above all operate by distorting the sensor from its normally-circular cross section to a shape approaching an oval or an ellipse. The Coriolis effect causes this elliptical pattern to "rotate" about the longitudinal axis of the cylinder/wineglass. The output of the device is measured by detecting this rotation or phase shift.
Although these prior art devices are to some degree functional for their intended purposes, these devices have numerous shortcomings. Among other things, the output from most of the devices is a relatively small scale factor with a large quadrature signal. Those skilled in the art will understand that this yields a large bias instability.
The wineglass gyros can provide good performance (sometimes comparable or perhaps even exceeding the performance characteristics of the present invention), but they typically are very expensive to fabricate, in part because they require tremendous precision during manufacture and assembly.
The present invention, in contrast, has a greatly reduced bias instability with relatively affordable manufacturing costs. The preferred embodiment of the invention utilizes separate drive and pickoff cylinders. The drive mode natural resonant frequency ("NRF") and the pickoff mode NRF are both high Q modes and are slightly separated (in the nominal range of 0.5 to 5%, but not limited to that range). These two different modes have NRFs that are close enough to be strongly coupled, which benefits the pickoff amplitude. Among other things, the strong coupling provides a much larger scale factor and greatly reduces quadrature signal. Certain embodiments of my invention thus provide a relatively high scale factor with a bias stability that is two orders of magnitude smaller than most prior art devices (with the exception of the expensive wineglass gyros, as noted above).